从与.class文件不同的目录中运行java.exe时发生NoClassDeffFoundError

Question

I'm trying to learn to run java apps from windows command line and I can't figure out one problem.

I have a simple class on my desktop:

public class Hello{
    public static void main(String[] args){
        System.out.println("1, two, three");
    }
}

If I run javac and java commands when I'm in my desktop directory in cmd everything is well, but if I go one directory back (so I won't be in the same directory as the .java and .class files) then my cmd directory is C:\\Users\\Tomas and my Hello.java and Hello.class files are in C:\\Users\\Tomas\\Desktop . I can run the command javac Desktop\\Hello.java and it works, but then if I try to do java Desktop\\Hello.java I get an Exception in thread "main" java.lang.NoClassDefFoundError: Desktop\\Hello (wrong name: Hello) .

I know that NoClassDefFoundError is throws when a class was available at compile time, but ClassLoader can't find it during run time ( found a good article about it here ). I think the problem has something to do with the CLASSPATH variable, so I set it to:

"C:\Program Files\Java\jdk1.7.0_21\jre\lib\ext";.;"C:\Program Files\Java\jdk1.7.0_21\jre\bin";"C:\Users\Tomas\Desktop"

(I included "C:\\Users\\Tomas\\Desktop" just to try everything) And I tried running the "java" command with -classpath and -cp options:

java -classpath "C:\Program Files\Java\jdk1.7.0_21\jre\lib\ext";.;"C:\Program Files\Java\jdk1.7.0_21\jre\bin";"C:\Users\Tomas\Desktop" Desktop\Hello

And I keep getting the same exception. I't would be great if someone can explain my error and why this is happening, and maybe point even give some directions where can I read more about this.

Thank you.

Answer 1

class

package Desktop;

public class Hello{
    public static void main(String[] args){
        System.out.println("1, two, three");
    }
}

compile (here Desktop means standart windows directory)

javac Desktop\Hello.java

execute (here Desktop means package . Desktop/Hello is fully class name)

 java Desktop/Hello

Answer 2

java -classpath 'C:\Users\Tomas\Desktop\Hello.class'

应该运行它。

Answer 3

Try java -classpath "C:\\Program Files\\Java\\jdk1.7.0_21\\jre\\lib\\ext";.;"C:\\Program Files\\Java\\jdk1.7.0_21\\jre\\bin";"C:\\Users\\Tomas\\Desktop" Hello

I only removed Desktop from your class name.